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Nasal ethmoid conchae: Are thin osseous scrolls that are covered on each side with m.m. are originated with a basal lamella from the lateral wall of the nasal cavity. This lamella projects medially like a shelf and is continued by one , two , or more spirals lamellae which roll up on themselves and form the scroll .The spiral lamellae enclose air filled recesses which communicate extensively with the nasal meatuses . Along their free border , the spiral lamellae may be form bullae or bubble which may in turn , be subdivided by small transverse septa into cells if the free border of spiral lamellae unites with basal lamellae or with adjacent facial bone , a conchal sinus results. Bullae , cells and a conchal sinus are never entirely seals off and communicated through small apertures with the nasal cavity. The large dorsal , middle and ventral nasal conchae are located in the large middle portion of the nasal cavity , while the smaller and more numerous ethmoidal conchae are in the caudal portion of the nasal cavity. The caudal part of the dorsal and middle nasal conchae are part of ethmoid labyrinth of the scrolls (ethmoid conchae)and are known as endoturbinatesI and П respectively . The large, and ventral nasal conchae project from the lateral wall and divide the nasal cavity into three meatuses . 1-The dorsal nasal meatus : is narrow passage between the roof of the nasal cavity and dorsal conchae and leads into the caudal part of the nose. 2- The middle nasal meatus: is between the dorsal and ventral conchae and its leads caudal part. In the carnivores and ruminant , this meatus is split caudally by the middle nasal concha into dorsal and ventral channels. 3-the ventral nasal meatus: -is the largest . lies between the ventral concha and the floor of the nasal cavity and leads into the nasopharynx. Most of the respiratory air passes through this meatus . 4-the common nasal meatus –the narrow space between the nasal septum and the conchae extends from the roof of the nasal cavity to the floor and is continuous laterally with the other meatus. Similar air spaces between the etmoid conchae are the ethmoid meatuses . In the rostral portion of the nasal cavity, the mucosa of the lateral wall forms a number of fold which extend from the nasal conchae to the nostril . 1-The straight fold –is continuous with the dorsal concha. Its double in the horse , but is united rostrally. 2-The alar fold—lies ventral to the straight fold. Its continuous with the ventral nasal concha and contains the supporting medial accessory cartilage. In horse its contains the lamina of the alar cartilage. 3-The basal fold –is most ventral. In the horse it originates from the ventral concha, but in the other species its independent of the concha and units rostrally with the alar fold. The ducts which open in the nasal cavity: 1-Incisive duct : or nasopalatine duct: Is paired tube in the floor of the nasal cavity which is directed rostroventrally and connects the nasal cavity with the oral cavity. The nasal opening is situated in the ventral meatus at the level of the canine tooth. The oral opening of the duct is on the incisive papilla caudal to the upper incisors. In horse, the duct does not open into the oral cavity, but ends blindly under the oral epithelium. 2-the lateral nasal gland: which is absent in ox and microscopic dimensions in the other domestic animals. In the pig and carnivores –it's in the maxillary sinus (recess) in the horse and small ruminant –its lies close to the nasomaxillry aperture. The duct runs a long the middle meatus and opens inside the nostril close to the straight fold or at the end of it. In the horse –the opening is at the level between the first and second tooth. Except in the horse, the secretion of the lateral nasal gland passes through the incisive duct into the oral cavity. The secretion helps moisten the inhaled air, and in the dog also the nose, and its also believed to play role in the functioning of the vomeronasal organ. 3-the opening of the nasolacrimal duct: is located in the flour of the nostril of the junction of the skin and mucosa. In pig there is second opening of the nasolacrimal duct located on the lateral surface of the ventral nasal concha near its caudal end. 4-the vomeronasal organ: consist of a pair of ducts which lie in the flour of the nasal cavity on either side of the nasal septum. The epithelium lining of ducts resembles that of the nasal cavity and contains elements of both the respiratory and olfactory regions. The ducts are supported by thin –walled cartilaginous sleeves (cartilaginous vomeronasales )but also by vomer.each tube extends caudally from their opening in the incisive duct at level of the canine teeth , to a level of the second or four cheek tooth , where they end blindly. The function of the vomeronasal organ to determine the flavor of food in the mouth by olfaction and smelling the liquid from the urine and vagina. Vessels and nerves: 1-artery –sphenopalatine a., ethmoidal branches from the ethmoid rate in the olfactory fossa,& branches of greater palatine artery. 2-viens: sphenopalatine., ethmoidal& palatine veins. 3-lymph vessels go to mandibular lymphnode and retropharyngeal lymphnode. 4-nerves: sensory from trigeminal nerve , (ethmoidal nerve from ophthalmic nerve and palatine nerve from maxillary nerve ).